The present invention relates to a vertical contour compensator in a television set, and more particularly to a motion-adaptive vertical contour compensator which compensates the vertical contour by adding an extra value corresponding to a motion state of an image after a double-conversion of a scanning line interpolated signal and an original signal.
As necessity of good images with the higher definition, ID (Improved Definition) systems in which a vertical scanning ratio was improved from 2 : 1 to 1 : 1 in conventional televisions such as NTSC, SECAM and PAL systems, ED (Extended Definition) systems in which a cancel function of a ghost image is added to a transmitter and a receiver, and HD (High Definition) systems in which the high definition is achieved by using a satellite broadcasting system have been under development.
Particularly, in a television of the ID system which is compatible with the conventional TV broadcasting system and obtains the image of high definition, the vertical contour compensation is carried out after the vertical scanning lines are doubled by an interpolation of motion-adaptive scanning lines.
In the conventional ID-TV, the contour compensation is performed as shown in FIG. 1. In FIG. 1, a luminance signal Y is separated by a Y/C separator 2 according to an output of a motion-detector 3 after converting an analog composite video signal into a digital signal by an A/D converter 1. A Y-processor 4 controls the contrast of the Y-signal and compensates horizontal and vertical contours of the Y-signal so that the luminance signal separated by the Y/C separator 2 and a Y-interpolator 5 interpolates the luminance. This Y-signal is doubled by a double-converter 7 so that a clock frequency is doubled. Then, the Y-signal is applied to a matrix 12 to provide R, G, and B (Red, Green, and Blue) signals after a digital-to-analog conversion of the Y signal by a D/A converter 9.
Similarly, a color signal C is processed through a C-processor 15, a C-interpolator 6, a double-converter 8, D/A converters 10 and 11, and the matrix 12. During the above process, necessary clock and control signals are provided from a synchronous-separator 13 and a control signal generator 14, respectively.
The conventional vertical contour compensation is carried out by the Y-processor 4 and the frequency characteristic of this case is shown in FIG. 2(a). This frequency characteristic reveals no correlation between the scanning lines at a screen of 0, 525/2 CPH (Cycles Per Height) in the vertical direction. Therefore, in a totally black (or all white) or periodically white-and-black screen, the scanning lines have no correlation to each other as shown in FIG. 2(b). In a screen of 525/4 CPH, the correlation reaches a maximum value B as shown in FIG. 2(b) (vertical detail).
Since the conventional vertical contour compensation has frequency characteristic as shown in FIG. 2(a), in case of scanning lines of 525/2 CPH in the periodical black-and-white screen, vertical contour compensation is impossible. In other words, the vertical contour compensation can not be expected in a screen which has an edge component along with the vertical direction.